A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In general, the positioning of both the substrate and the patterning device is provided by positioning devices that include one or more electromagnetic motors or actuators, such as linear or planar motors. Such motors typically comprise a coil assembly comprising one or more coils, arranged to co-operate with a magnet assembly that typically comprises an array of permanent magnets providing an alternating magnetic field distribution. In general, these magnets are mounted to a support structure such as a magnetic support structure (e.g. including a ferromagnetic yoke) after being magnetized. Once magnetized, care should be taken in the handling of such permanent magnets as the magnets may be subject to comparatively large forces when brought near other magnets or magnetic structures such as ferromagnetic support structures.
Further, it should be noted that, once magnetized, the processing of such magnets may be restricted. As an example, an accurate machining of the magnets may be difficult if not impossible as a result of the forces exerted by the magnets. Further, in order to avoid de-magnetization, heat treatments of the magnets may be subject to limitations, such limitation e.g. resulting in an extended manufacturing time.